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Suppose we have lost all the datafiles, logfiles and even control file and
parameter file is also lost.

This usually happens when the Primary Disk is damaged

Then to recover the database from this kind of failure we need to do
disaster recovery or full database recovery

Assumption

All datafiles and logfiles are lost

The database was running in Archivelog mode

Control file and SPFILE is also lost

RMAN backups of the database is available

We were not using RMAN with recovery catalog

To restore and recover the database do the following

Step 1

If you have lost the primary disk where O/s and Oracle was installed.
Then, install a new disk and format and install the same operating
system and same version of Oracle database software which was install
before failure

Step 2

Make sure RMAN backups are available and also make sure archive log
files of this database are also accessible

Start RMAN by typing the
following command

$ export ORACLE_SID=test$ rman target / nocatalog

Now the most important thing we need to do now is to set the database ID
(DBID) at RMAN prompt. The DBID uniquely identifies the database.

If you have already noted down the DBID of the database then you can
straight forward type the DBID at the RMAN prompt.

Otherwise if you have not noted down the DBID then the other ways you
can get the DBIDx is

If you have turned ON the autobackup of Controlfile and
configured the AUTOBACKUP filename to contain the DBID then you can
look into the directory where Controlfile AUTOBACKUP files are
located. Usually the directory set with the path
DB_RECOVERY_FILE_DEST parameter. The control files auto backup files
will have the DBID in the format
c-IIIIIIIIII-YYYYMMDD-QQ

Where

IIIIIIIIII stands for the DBID.

YYYYMMDD is a time stamp of the
day the backup is generated.

QQ is the hex sequence that
starts with 00 and has a maximum
of FF.

If you have ever recorded the output of RMAN session previously
then you can look into that output text file. The RMAN will always
show the DBID when it is connected to the database as shown below